Graphene nanoplatelet metal matrix

ABSTRACT

A metal matrix composite is disclosed that includes graphene nanoplatelets dispersed in a metal matrix. The composite provides for improved thermal conductivity. The composite may be formed into heat spreaders or other thermal management devices to provide improved cooling to electronic and electrical equipment and semiconductor devices.

FIELD

This disclosure relates generally to a composite materials, and moreparticularly to metal matrix composites including graphenenanoplatelets.

BACKGROUND

Highly conductive metals have been used to form conducting componentssuch as heat spreaders and heat sinks for high power electronicpackaging and other thermal management applications. In someapplications, metal matrix composites (MMC's) formed by addingparticulate fillers to a metal matrix have been used to optimize theproperties of a conducting component to suit the requirements of aparticular application. By properly selecting a particulate filler and ametal matrix, material properties can be controlled. For example, SiCparticles have been added to an aluminum matrix to improve thecoefficient of thermal expansion (CTE), stiffness, and wear resistanceas compared to pure aluminum. However, in general, the thermalconductivity of Al/SiC MMC's do not meet desired expectations.Additionally, graphite and carbon nanotube MMC's have been developed.However, these MMC's can experience mechanical stress problemsassociated with the poor shear stress characteristics. Furthermore,carbon nanotubes are an expensive filler material.

There is a need for an improved material for conducting heat away fromheat generating components such as semiconductor devices.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems and methods that are meant to beexemplary and illustrative, not limiting in scope. In variousembodiments, one or more of the limitations described above in theBackground have been reduced or eliminated, while other embodiments aredirected to other improvements.

A first embodiment of the disclosure includes a composite including ametal matrix and uniformly oriented graphene.

A second embodiment of the disclosure includes a semiconductor packageincluding a thermal management member and a semiconductor device. Thethermal management member includes a metal matrix and graphene.

A third embodiment of the disclosure includes a method of forming agraphene metal matrix composite including the steps of forming asubstantially uniformly oriented graphene layer, and forming the metalmatrix composite by including the substantially uniformly orientedgraphene layer in the metal matrix.

One advantage of the present disclosure is to provide a MMC withsubstantially improved thermal conductivity.

Another advantage of the present disclosure is to provide a compositehaving improved thermal conductivity-to-weight ratio than graphite orcarbon nanotube embedded metal matrix heat spreaders.

Another advantage of the present disclosure is to provide a compositehaving improved mechanical stress issues as compared to MMC's withgraphite.

Another advantage of the present disclosure is to provide a low costMMC.

Another advantage of the present disclosure is to provide a novelprocess to produce graphene metal matrix composite thermal managementcomponents.

Yet another advantage of the present disclosure is to provide a reducedweight thermal management system.

Further aspects of the method and apparatus are disclosed herein. Otherfeatures and advantages of the present disclosure will be apparent fromthe following more detailed description of the preferred embodiment,taken in conjunction with the accompanying drawings that illustrate, byway of example, the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary graphene nanoplatelet according to thedisclosure.

FIG. 2 is an exemplary embodiment of a metal matrix composite accordingto the disclosure.

FIG. 3 illustrates a exemplary process for forming a graphene metalmatrix composite according to the disclosure.

FIG. 4 is an exemplary embodiment of a semiconductor package simplifiedfor relative comparison according to the disclosure.

FIG. 5 illustrates a thermal analysis result for an exemplarygraphene/aluminum matrix.

FIG. 6 illustrates comparative thermal analysis results for asemiconductor package.

FIG. 7 illustrates other comparative thermal analysis results for asemiconductor package.

DETAILED DESCRIPTION

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawing, in which a preferred embodimentof the disclosure is shown. This disclosure may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe scope of the disclosure to those skilled in the art. All compositionpercents are volume percent, unless otherwise specified.

According to the present disclosure, a MMC is disclosed that includes ametal matrix and graphene nanoplatelets. The metal matrix may be ahighly conductive metal or metal alloy. In one embodiment, the metalmatrix may be selected from a group including copper, aluminum andalloys, thereof.

Graphene is a one-atom-thick planar sheet of sp²-bonded carbon atomsthat are densely packed in a honeycomb crystal lattice. Graphene has adensity of approximately 1.7 g/cm³. Graphene nanosheets or nanoplateletsare formed from layers of graphene.

FIG. 1 illustrates a graphene nanoplatelet 10 according to an embodimentof the present disclosure. As can be seen in FIG. 1, the graphenenanoplatelet 10 has a length (L) along the X axis, a width (W) along theY axis, and a height (H) along the Z axis. In other words, the L and Wlie in the X,Y plane. The L and W are the major dimensions of thegraphene nanoplatelet 10, or in other words, the graphene nanoplateletis oriented in the X,Y plane. In one embodiment, the L and W may beabout 50 nanometers (nm) to about 20 mm (millimeters). In yet anotherembodiment, the L and W may be about 200 nm to about 5 microns (μm). Inyet another embodiment, the L and W may be about 300 nm to about 2 μm.In yet another embodiment, the L and W may be about 1 mm to about 20 mm.Graphene nanoplatelets 10 have a thermal conductivity of about 5,300watts/(meter×degree Kelvin) (W/mK) in the X-Y plane.

In this exemplary embodiment, the graphene nanoplatelet 10 has arectangular geometry in the X,Y plane. In another embodiment, thenanoplatelet 10 may have other geometries in the X,Y plane, including,but not limited to square, oval, and hexagonal. The present disclosureproposes that larger X,Y planar dimensions are desirable, and asnanoplatelet formation technology develops, larger platelet sizes arecontemplated and considered within the scope of this disclosure.

In one embodiment, the graphene nanoplatelets 10 have an average H inthe Z direction of less than about 10 nanometers (nm). In anotherembodiment, the graphene nanoplatelets 10 have an average H of less thanabout 5 nm. In still another embodiment, the graphene nanoplatelets 10have an average H of less than about 2 nm. In another embodiment, thegraphene nanoplatelets 10 have an average H of less than about 1 nm. Inyet another embodiment, the graphene nanoplatelets 10 have an average Hof less than about 0.5 nm.

In another embodiment, the graphene nanoplatelets 10 have an average Hof about three atomic layers. In another embodiment, the graphenenanoplatelets 10 have an average H of about 2 atomic layers. In yetanother embodiment, the graphene nanoplatelets 10 have an average H ofabout 1 atomic layer.

FIG. 2 illustrates an exemplary graphene metal matrix composite(composite) 100 according to the disclosure. In this exemplaryembodiment, the composite 100 has a plate or sheet geometry. Thecomposite 100 includes a metal matrix 110 and graphene nanoplatelets120. The graphene nanoplatelets 120 are substantially uniformly orientedin the X-Y plane in layered grids or sheets 125 that are substantiallyuniformly distributed in the metal matrix 110. The graphene 125 isuniformly oriented in the metal matrix 100. The metal matrix 110 may bea highly conductive metal or metal alloy. In one embodiment, the metalmatrix 100 is selected from the group including copper, aluminum, copperalloys, and aluminum alloys.

In one embodiment, the composite 100 includes graphene nanoplatelets 120in an amount of about 2 volume percent (vol %) to about 90 vol %. Inanother embodiment, the composite 100 includes graphene nanoplatelets120 in an amount of about 5 vol % to about 60 vol %. In still anotherembodiment, the composite 100 includes graphene nanoplatelets 120 in anamount of about 5 vol % to about 30 vol %. In yet another embodiment,the composite 100 includes graphene nanoplatelets 120 in an amount ofabout 5 vol % to about 10 vol %. In still another embodiment, thecomposite 100 includes graphene nanoplatelets 120 in an amount of about10 vol %.

An expanded view of the composite 100 is shown in 100A. As can be seenin 100A, the grid sheets 125 include horizontal grids 122 and verticalgrids 124. The horizontal grids 122 enhance thermal conductivity in theX,Y plane or X,Y directions. The vertical grids 124 enhance thermalconductivity in the Z direction. The horizontal grids 122 have the majornanoplatelet dimension or axis in the X,Y plane and thickness in the Zdirection. The vertical grids 124 have the major nanoplatelet dimensionin the Z direction and thickness in the X,Y plane. The horizontal grids122 and the vertical grids 124 substantially orient the graphenenanoplatelets 120 in two perpendicularly oriented directions. When theratio of horizontal grids 122 to vertical grids 124 is high, as shown inFIG. 2, the graphene nanoplatelets 120 provide for increased heattransfer in the X direction compared to the matrix metal. For example,the ratio of horizontal grids 122 to vertical grids 124 may be more thanabout 90%. In another embodiment, the graphene nanoplatelets 120includes only horizontal grids 122.

According to the present disclosure, graphene nanoplatelets (with athermal conductivity of about 5,300 (W/mK) in the X-Y plane) areuniformly distributed in a metal matrix, such as, but not limited tocopper (with a thermal conductivity of 400 W/mK) or aluminum (with athermal conductivity of 273 W/mK) to increase thermal conductivity overthe matrix metal in the orientation plane of the graphene nanoplateletswhile reducing its weight. Thus, the disclosure produces a compositehaving an increased thermal conductivity-to-weight ratio than the matrixmetal. In one embodiment, an about 10 vol % graphene Al composite has athermal conductivity of about 713 W/mK. In another embodiment, an about10 vol % graphene Cu composite has a thermal conductivity of about 860W/mK.

A graphene metal matrix composite can be manufactured according to anyof the following exemplary processes. The graphene nanoplatelets areprovided in dry form or in dispersed form in solvents. The graphenenanoplatelets, if not provided in a solvent, are dispersed in a solventwith a low evaporation temperature such as acetone or alcohol.

The graphene nanoplatelets in solvent are poured over a thin mesh. Thegraphene nanoplatelets are captured on the mesh in a planar direction.The carrier solvent is completely removed by heating to form a graphenelayer. The mesh may be a metal or polymer. In one embodiment, the meshis the same metal as the matrix metal. In this case, the mesh will notbe removed for further processing. In another embodiment, the mesh maybe formed of a removable material, such as a polymer or organicmaterial. In this embodiment, the mesh is removed, such as by heating orsolvent extraction, before or during further processing to form agraphene layer.

The graphene layer is filtrated by a suitable method, such aselectrolytic/electro-less plating, evaporation, or sputtering, to form athin layer of metal-graphene composite. In one embodiment, the metal isaluminum or copper. By repeating the steps, multiple layers are made andformed into a composite building block. Layer stacking of buildingblocks is performed next to form a composite block having a targetedthickness. In one embodiment, a composite block including bothhorizontal and vertical layers may be formed by stacking building blocksto provide for both orientations of the graphene nanoplatelets.

The composite block is subsequently hot and/or cold worked to reach afinal thickness and density. In one embodiment, the composite block ishot pressed, formed and cold rolled to reach the final thickness.Shaping may then be performed to achieve a desired shape. For example,sawing and machining may be performed to manufacture a plate having adesired shape and size.

According to another exemplary process, the graphene composite can beformed by hot melting and extrusion of a graphene/metal mix. In thiscase, the alignment of graphene nanoplatelets is primarily achievedthrough mechanical force flow.

According to yet another exemplary process, a graphene composite isformed by forming graphene layers in a loosely connected thin sheet formby attaching graphene to the surface of sacrificial material which canbe removable easily either by heating or chemicals, then infiltratingthe loosely connected thin sheet form with a metal matrix by hot melt orelectrolytic/electrolysis plating to form a composite building block.The composite building blocks are subsequently processed as describedabove, for example including the steps of stacking, hot pressing, coldforming and machining. In yet another embodiment, a graphene compositewas formed using graphene sheets and conventional power metallurgicalprocessing.

FIG. 3 illustrates a exemplary process for forming a graphene metalmatrix composite including the steps of providing graphene nanoplateletshaving a thickness of less than about 100 nm 310; forming asubstantially uniformly oriented graphene layer 320; orienting thesubstantially uniformly oriented graphene layer in a first plane with amatrix material 330; orienting a second substantially uniformly orientedgraphene layer in a plane substantially perpendicular to the first plane340; forming a metal matrix composite containing the substantiallyuniformly oriented graphene in a metal matrix 350; heating the metalmatrix composite to form a substantially dense metal matrix composite360; and mounting a semiconductor device on the metal matrix composite370. In one embodiment, the metal matrix is aluminum or copper.

In any of the above processes, a small amount of impurities, for examplefor alloying purpose, can be added at the hot melt stage or anysubsequent step for cost effective manufacturing. All of thesemanufacturing techniques are amenable to and are expected to beautomated, for example in a roll-to-roll conveyor system. Theroll-to-roll manufacturing process is typically cheaper thanconventional batch mode processing.

FIG. 4 illustrates an exemplary semiconductor package 200 including athermal management member 210 and a semiconductor device 220 mounted atthe center of the thermal management member 210 according to thedisclosure. The thermal management member 210 is a thermal managementplate. In other embodiments, the thermal management member may beselected from a group including, but not limited to avionics chassis,heat spreaders, equipment enclosures, cold plates, rack, trays, shelf,heat sinks, heat exchanger, radiators, and heat pipes. The semiconductordevice is a semiconductor chip. In other embodiments, the semiconductordevice may be any heat generating semiconductor component, such as, butnot limited to microprocessor, power inverter/converter, solid stateswitch, Application Specific Integrated Circuit (ASIC), graphicsaccelerator chip, and Insulated Gate Bipolar Transistor (IGBT).

In one example, simulations were performed using a thermal managementmember 210 having a width (W) in the Y direction of 76 cm, a length (L)in the X direction of 76 cm, and a thickness or height (H) in the Zdirection of 0.5 cm, and a semiconductor chip 220 having a 100 W poweroutput and having a width (w) in the X direction of 1 cm and a length(l) in the X direction of 1 cm. For these simulations, runs wereperformed for a thermal management member 210 formed of aluminum,copper, aluminum and 10 vol % graphene, and aluminum and 10 vol %graphite. In these simulations, the graphene platelets were horizontallyoriented, or in other words, oriented with maximum dimensions in the X-Yplane thickness of the platelets in the Z direction. For thesesimulations, forced air cooling was provided at a rate of 60 W/m²K asindicted by the diagonal arrows B and ambient air convection wasprovided at a rate of 6 W/m²K as indicated by the vertical andhorizontal arrows C. FIG. 5 shows the results of the simulation foraluminum and 10 vol % graphene.

FIG. 6 shows the comparative results of the simulation for the materialschosen. In FIG. 6, straight line plots of from the center point to theedge point are shown for simplicity. As can be seen in FIG. 6, thealuminum and 10 vol. % graphene composite outperformed the othermaterials by maintaining the lowest temperature at the center of thethermal management member 210 member. This reflects the increasedthermal conductivity of aluminum and 10 vol % graphene thermalmanagement member compared to the other materials.

FIG. 7 shows the results of the simulation for aluminum, copper, copperand 10 vol % graphene, and copper and 10 vol % graphite, again shown asstraight line plots for simplicity. As can be seen in FIG. 7, the copperand 10 vol % graphene outperformed the other composites by maintainingthe lowest temperature at the center of the thermal management plate andby most rapidly decreasing the temperature away from the center. Thisreflects the increased thermal conductivity of copper and 10 vol %graphene thermal management plate compared to the other materials.

The above compositions and processes may be used to form various heattransfer components, such as, but not limited to include avionicschassis, heat spreaders, equipment enclosures, cold plates, rack, trays,shelf, heat sinks, heat exchanger, radiators, and heat pipes. In thesevarious structures, the nanoplatelets are oriented to promote heattransfer in a particular direction based on the structure orientationand use.

While the disclosure has been described with reference to exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiments disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims. It is therefore intended that the following appendedclaims and claims hereafter introduced are interpreted to include allsuch modifications, permutations, additions, and sub-combinations as arewithin their true spirit and scope.

1. A composite, comprising: a metal matrix; and substantially uniformlyoriented graphene.
 2. The composite of claim 1, wherein the graphenecomprises graphene nanoplatelets having a thickness of less than about100 nm.
 3. The composite of claim 1, wherein the graphene comprisesgraphene nanoplatelets having a thickness of less than about 1 nm. 4.The composite of claim 1, wherein the metal matrix is selected from agroup comprising copper and aluminum.
 5. The composite of claim 1,wherein the graphene is substantially uniformly horizontally oriented inthe metal matrix.
 6. The composite of claim 1, wherein the compositecomprises between about 2 vol % and about 90 vol % graphene.
 7. Thecomposite of claim 1, wherein the composite comprises between about 5vol % and about 20 vol % graphene.
 8. A semiconductor package,comprising: a thermal management member, and a semiconductor device;wherein the thermal management member comprises: a metal matrix; andgraphene.
 9. The package of claim 8, wherein the graphene comprisesgraphene nanoplatelets having a thickness of less than about 100 nm. 10.The package of claim 8, wherein the metal matrix is selected from agroup comprising copper and aluminum.
 11. The package of claim 8,wherein the graphene is uniformly distributed in the metal matrix. 12.The package of claim 8, wherein the composite comprises between about 2vol % and about 90 vol % graphene.
 13. The package of claim 8, whereinthe thermal management member has a plate geometry.
 14. The package ofclaim 8, wherein the thermal management member is selected from thegroup consisting of avionics chassis, heat spreaders, equipmentenclosures, cold plates, rack, trays, shelf, heat sinks, heat exchanger,radiators, and heat pipes.
 15. A method of forming a graphene metalmatrix composite, comprising: forming a substantially uniformly orientedgraphene layer; forming the metal matrix composite including thesubstantially uniformly oriented graphene layer within the metal matrix.16. The method of claim 15, further comprising: providing graphenenanoplatelets having an average thickness of less than about 100 nm toform the first substantially uniformly oriented graphene layer.
 17. Themethod of claim 15, further comprising: orienting the substantiallyuniformly oriented graphene layer in a first plane within a matrixmaterial.
 18. The method of claim 17, further comprising: orienting asecond substantially uniform oriented graphene layer in a planesubstantially perpendicular to the first plane.
 19. The method of claim15, further comprising: heating the matrix metal composite tosubstantially densify the metal matrix composite.
 20. The method ofclaim 15, further comprising: mounting a semiconductor device on themetal matrix composite.